Journal of the Turkish Chemical Society Section A: Chemistry

Öz

Copper and copper based alloys are of considerable importance as they form the
backbone of modern industries. Brass has been widely used for shipboard condensers, power plant condensers and petrochemical heat exchangers [1]. Thiadiazoles which are important compounds in many fields were reported earlier as corrosion inhibitors for metals and their alloys [2-8]. Recently, Joseph Raj at al. [9] was experimentally investigated the inhibition efficiencies of three amino thiadiazole derivatives for brass in natural seawater as shown in Figure 1. The relationships between the quantum chemical parameters and corrosion inhibition of those compounds have not been studied yet. 
In this study, corrosion inhibition efficiencies of three amino thiadiazole derivatives namely 2-amino-5-etil-1,3,4-thiadiazole (AETD), 2-amino-5-etiltiyo-1,3,4-thiadiazole (AETTD) and 2-amino-5-ter-butil-1,3,4-thiadiazole (ATBTD) as corrosion inhibitors on brass known as copper alloy in both gas and water phase were investigated by using B3LYP/6-31G(d,p) and B3LYP/6-31++G(d,p) basis sets by DFT method. Quantum chemical parameters such as the highest occupied molecular orbital energy (EHOMO), the lowest unoccupied molecular orbital energy (ELUMO), energy gap (ΔE= ELUMO - EHOMO), sum of the total negative charge (TNC), electronegativity (χ), global hardness (ɳ), softness (ϭ), the fraction of electrons transferred (ΔN) and proton affinity (PA) were calculated. Furthermore, the interaction energies of the investigated amino thiadiazole derivatives with the copper metal were obtained. The effect of substituent types and its positions on the thiadiazole ring were investigated for all structures. As a results, the inhibition efficiency of investigated amino thiadiazole derivatives was observed to increase with increasing the electron donor characteristic of the substituted groups. A good correlation was found between the quantum chemical parameters and experimental inhibition efficiencies of the investigated amino thiadiazole derivatives.